1. Field of the Invention
The present invention relates to a process for depositing metals, and in particular copper, on a substrate.
2. Description of Related Art
The deposition of metals, and in particular of copper, on substrates has an advantage, in particular in the following cases:                it makes it possible to promote the wetting of the substrates, for example if the latter must be incorporated into a liquid matrix,        it enables metal-ceramic brazing by pre-metallization of the ceramic,        it makes it possible to optimize the electrical and/or thermal conductivity of surfaces of insulating materials.        
The deposition of metals, and in particular of copper, on substrates can be carried out via various techniques:
i) by physical vapor deposition (PVD): this process consists, for example, in carrying out a sputtering of the metal in a reactor in which the substrate to be coated is placed. The application of a potential difference between the target (cathode) and the walls of the reactor within a rarefied atmosphere enables the creation of a cold plasma. Under the effect of the electric field, the positive species of the plasma are attached by the target and collide with the latter. They then pass on their momentum, thus giving rise to the sputtering of the metal atoms in the form of neutral particles which condense on the substrate in order to form a metallic film thereon. This type of technique is, for example, described in A. Billard and F. Perry, “Pulvérisation cathodique magnetron” [Magnetron sputtering], Techniques de l'Ingénieur, Traité de Matériaux, M 1 654-1.
ii) by chemical vapor deposition (CVD): according to this technique, the substrate is exposed to one or more metal precursors in the gas phase, which react and/or decompose at the surface of the substrate in order to generate the deposit of metal (S. Audisio, “Dépots chimiques à partir d'une phase gazeuse” [Chemical depositions from a gas phase], Techniques de l'Ingénieur, Traité de Matériaux, M 1 660-1). The deposition may be plasma-enhanced.
The PVD and CVD deposition techniques require sophisticated and expensive equipment. Furthermore, they cannot be adapted to any type of support. They also have the drawback of using polluting solvents.
iii) by aqueous chemical deposition: it generally consists in carrying out a redox reaction in an aqueous medium in the presence of a catalyst. The product of the reaction is adsorbed on a substrate in order to form a thin metal film thereon. However, aqueous chemical deposition does not allow a selective deposition of metal on certain zones of the substrate for example. The deposit made is not always sufficiently well fastened to the substrate (simple adsorption).